Paralleling relay system



Dec. 30, 1930. P. THOMAS i 1,736,792.

PARALLELING RELAY SYSTEI Filed Feb. 1. 1928 Line /80 Phase 1909/2 Leoa. 06 Phase I909/e 4 L09. l80

INVENTOR Phi/bps 7770/1705.

ATTORNEY Patented Dec. 30, 1930 UNITED STATES PATENT OFFICE PHILLIPS THOMAS, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 80 MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA PARALLllilIlIN'Gr RELAY SYSTEM Application filed February 1, 1928. Serial No. 251,076,

This invention pertains to a system for automatically paralleling two alternatingcurrent circuits, and the object hereof is to provide a suitable system of relays and control circuits for automatically connecting two such circuits in parallel when the voltages thereof are equal and in synchronism.

A further object of my invention is toprovide a paralleling relay system whereby the operationof the means forv connecting the circuits in parallel will be initiated at a time in advance of the occurrence of synchronism between the voltages of the circuits.

, A further object of my invention is to provide a paralleling relay system by which the operation of the circuit-connecting means will be initiated in advance of the occurrence of synchronism by a'time interval which is proportional to the dilference in the frequencies of the circuits.

In my copending applications Serial No. 227,461 filed Oct. 20, 1927 (Case #155,464), and Serial No. 221,490 filed Sept. 23, 1927 (Case #13,489), which have matured into Patents No. 1,732,734, issued Oct. 22, 1929, and No. 1,7 34,239, issued Nov. 5, 1929, respectively, I have disclosed paralleling relay systems which operate to initiate the closing of a paralleling switch in advance of the occurrence of synchronism by a predetermined time desirable, since it automatically compensates for various beat frequencies. The systems disclosed in my copending' application operate to close the paralleling breaker exactly at synchronism only when the beat frequency is of a predetermined value, but the system of the present application willpermit the closing of the paralleling breaker exactly at synchronism whatever the beat frequency happens to be. The desirability. of the system about to be described is apparent from a consideration of the fact that when the beat fre-j quency is high, the approach of the voltagevectors to the position at which they coincide is rapid, and for that reason the operation of the paralleling breaker must be initiated in advance of actual synchronism bya time interval which is greater than when the beat frequencyis low, underwhich condition the closing operation need. not be initiated until the voltage vectors are nearly coincident...

According to myinvention, I propose to make use of transformers having primary and secondary alternating-current windings and direct-current saturating windings. These transformers are well known in the art, and operate on the principle that the superposition of aunidirectional flux upon an alternating flux in a magnetic circuit reduces the effective reactance of the winding inducing the alternating flux, and, therefore,the voltage induced therein, or in other words, increases the magnetizing current. 3 1

By means of suitable transformers connected as shown, I obtain a voltage proportional to the vector difi erence of the volt-- ages of the two circuits to be paralleled. Direct currents proportional to the vector difference of the said volta es are obtained 1 from rectifiers energized by voltage obtained from said transformers, and the direct-current saturating windings of the transformers above mentioned are energized thereby. Suitable means are provided for delaying the variations in the alternatingcurrent voltage of one of said transformers, resulting from a variation in the energization of the direct-currentwinding. Another similar transformer is so connected that the variation of its alternating-current voltage follows that in the energization of the directcurrent winding instantaneously.

Direct currents proportional to the voltages across the secondary windings of said transformers are supplied to opposing direct-current windings of a third trans former, the alternating-current voltage of which is cont-rolled by the net magnetization induced by the dilfeQt-0urrent windings.

The voltage across the alternating-current windings of the third transformer, in turn, energizes a relay to cause the closing of the paralleling switch.

As will be explained more fully hereinafter, the voltage across the. secondary winding of the last-mentioned transformer becomes suflicient to operate the paralleling relay in advance of the occurrence of synchronism, by a time interval which is proportional to the beat frequency, or the difference in the frequencies of the two alternating current circuits.

For a complete understanding of my invention reference should be had to the accompanying drawings, in which Figure 1 is a diagram illustrating the apparatus and circuits comprising the sys tem employing my invention; and

Fig. 2 illustrates graphically the variation of the voltages in different parts of the systern.

Referring to Fig. 1, two alternating-current circuits are indicated at l and 2. These circuits will generally be connected, respectively, to a distribution system and to a gen erator which it is desired to connect in parallel therewith.

This parallel connection may be accomplished by the operation of a switch 3.

For obtaining a voltage proportional to the vector difference of the voltages of the alternating-current system and the generator, I provide auto-transformers 1 and 5 between the midpoints of which are connected, in parallel, the primary windings of transformers 6 and 7. The secondary windings of these transformers are connected to rectifiers S and 9, which are illustrated as full wave rectifiers of the copper-oxide-disl: type, disclosed in U. S. Patent #1,640,335 to Grondahl, granted August 23rd, 1927. Any other suitable type of rectifier, however, may be substituted for that shown.

The direct-current terminals of the rectifiers 8 and 9 are connected respectively to direct-current windings 10 and 11 on the center legs of the cores of transformers 12 and 13. The transformers 12 and 13 are also provided with alternating current exciting or primary windings 14: and 15. These windings are energized from any suitable alternating current source, as an example of which the alternating-current generator 16 is shown. Rheostats 17 and 18 are connected in series with the exciting windings 14L and 15, respectively, to control the energization thereof.

The center leg of the reactor 12 is also provided with a lag winding 19, which is shortcircuited by a rheost-at 20. The purpose of this winding 19 is to delay the variation in the voltage across the alternating-current windings of the transformer 12 for a variable time interval after the variation in the energization of the direct-current winding 10, by setting up a magnetomotive force in opposition to any change in the magnetization of the transformer core.

The transformers 12 and 13 are also furnished with alternating-current windings 21 and 22, respectively, which perform the function of the secondary windings of the transformers, the windings 1 1 and 15 of the transformers serving as the primary windings. Obviously, the primary and secondary windings of the transformers 12 and 13 may be continuous in the manner of auto-transformers, and, instead of having a separate secondary, suitable taps on the single winding of the auto-transformer may be provided.

Rectifiers 23 and 24: similar to those shown at 8 and 9 are connected to the secondary windings 21 and 22. The direct-current terminals of the rectifier 20 are connected to a winding 25, and the direct-current terminals of the rectifier 2 1 are connected to a winding 26, on the center leg of a third transformer 27.

As shown transformer 27 is provided with a primary exciting winding 28 and a secondary winding 29. The primary winding 28 is connected in series with a rheostat 30 to the alternating-current generator 16.

The secondary winding 29 of the transformer 27 is connected to the alternating-current terminals of a rectifier 81, the direct-current output of which is supplied to the operating coil of a paralleling relay 32 having a contact 33 which is closed when the operating coil of the relay is energized.

When. the contact 33 is closed a circuit through a battery 34 and the operating coil of the paralleling switch 3 is completed and the switch 3 is closed to connect the circuits 1 and 2 in parallel.

Having described the equipment and the circuits necessary to perform the objects stated in the beginning of this specification, I shall now outline the method of operation of my system in the course of which description I shall refer to the curves shown in Fig. 2 to bring out more clearly the theory underlying my invention.

If the alternating-current circuit- 1 is assumed to be connected to a distribution circuit, it may be assumed that it will be energized from some other source (not shown). When it becomes desirable to connect the generator, to which. the circuit 2 is connected. in parallel with the distributicm circuit to supply energy thereto, the generator started and brought up to synchronous speed in the usual manner.

hen the circuit 1 is energized and the generator connected to circuit 2 is running at synchronous speed, and generating normal voltage, a voltage proportional to the vector difference of the line and the generator voltages will be impressed upon the primary windings of the transformers 6 and 7,, and a and 11, of the transformers 12 and 13 are (lo-energized, the reactance of the windings 14 and 15 is high, and the current therethrough is small, so that a high voltage exists across the windings Hand 15 and only a small voltage across active portions of the rheostats 17 and 18. -When the direct-current windings 10 and 11 are energized however, the magnetic circuit of the transformers is saturated to such an extent that the effective reactance of the windings 1 1 and 15 is decreased, and consequently a larger current flows from the source 16 through the rheostats and the exciting windings.

The increase in the exciting current resulting from the superposition of the unidirectional flux upon the alternating flux causes the distribution of the voltage drop across the rheostats and exciting windings to be changed so that the voltage across the winding 14 is now small compared to its original value, whereas the drop across the rheostat is increased. Obviously, the voltage drop across the secondary windings 21 and 22 is proportional to that across the exciting or primary windings 14: and 15.

The exciting windings 14 and {15 are distributed equally on the two halves of the cores of the transformers so that when the directcurrent windings 10 and 11 are tie-energized there will be no flux in the center legs of the transformers and consequently no alternating voltage will be induced in the direct-current windings. Y I

The lag winding 19, in connection with the rheostat 20, provides a closed circuit linking the flux in the center leg of the core of reactor 12. This closed circuit serves to oppose and delay for a limited time, depending upon the adjustmentof the rheostat 20, any change in the magnitude of the flux in the center leg of the reactor. The function of the winding 19, as previously pointed out, is to delay the changes in the magnetization of the reactor core resulting from changes in the energizetion of the direct-current winding 10.

If the direct-current winding 10 is energized by a steady current of a predetermined value, the voltage across the secondary windmg 21 Wlll be reduced from its normal high value to a value considerably lower, but the 1 reduction in the voltage across the secondary winding 21 will not take place until the lapse of a predetermined time after the energization of the winding 10. If the winding 10 is energized by a pulsating direct-current of low frequency, the voltage across the secondary winding 21 will rise and fall in accordance with the rise and fall of current in the wind ing 10, but the variations in the voltages of the winding 21 will be delayed for a predetermined time after the changes in energization of the winding 10 which give rise thereto.

If the frequency of the pulsations of directcurrent is low, the result just described will occur. If the frequency of the direct-current pulsations is high, however, it is obvious that the action of the winding 19 is such as to prevent the voltage across the winding 21 from reaching a value comparable with the value it would attain when the winding 10 is tie-energized. Thus it may be stated that the maximum value attained by the voltage across the winding 21 varies in accordance with the frequency of the direct-current pulsations energizing the winding 10, assuming that these pulsations are of uniform magnitude.

The variations in the voltage across the secondary winding 22 of the transformer 13.

are not delayed, as are the variations, in the voltage across the winding 21, but follow exactly the variations in the energization of the winding 11, since no lag winding is employed.

In 2, the curve A illustrates the variation of the'vol't-age across the alternatingcurrent secondary winding 22 of transformer 15 with the variation in the phase angle between the line and generator voltages, and is the same for all values of the beat frequency.

lNhen the line and generator voltages are in phase opposition, the voltage on the trans formers 6 and is a. maximum, the directcurrent windings 10 and 11 are fully energized, and the voltage across the alternatingcurrent secondary windings 21 and 22Vis a minimum." When the line and generator voltages are in phase, however, the voltage on the transformers 6 and 7 is substantially zero, the windings 10 and 11 are de-energized, and the voltages across the windings 21 and 22 are at their maximum.

Since the direct-current voltage of the rectifier 2 1 varies directly with the alternating-current voltage across the winding 22 of the transformer 13, curve A, which represents the alternating current voltage will also illustrate the direct-current voltage of the rectifier 24 The curve B illustrates the variation in thevoltage across the alternatingcurrent winding 21 of the transformer 12 (or, in thevoltage across the direct-current terminals of the rectifier 23) with the variation in phase angle between the line and the generator voltages, when the latter have the same frequency, or, in other words when the beat frequency is zero. It will be noted that curves A and B have the same maximum value, but the lowest point on curve A is lower than the corresponding point on curve B. This is a result of the design characteristics of the transformer 12. When the beat frequency is zero, the short-circuited or lag winding 19 is ineffective to delay the variations in the volt age-across the winding 21 of the transformer 12, since the winding 10 is energized by a steady direct current, the value of which depends on the phase angle between the line and generator voltages. \Vhen this angle is zero, the resultant voltage is zero, the winding 10 is (lo-energized, and the voltage across the alternating-current windings of the transformers are a maximum.

The curve C in Fig. 2 illustrates the variation in the direct-current voltage of the rectifier 23 for a given beat frequency. As already explained, the direct-current voltage of the rectifier 23, which is proportional to the voltage across the secondary winding 21, varies in accordance with the energization of the winding 10, which varies in accordance with curve B, but at a definite time interval thereafter. Thus the curve C reaches a maximum at a definite time after the curve A reaches its maximum and furthermore, the maximum value of the curve C is lower than that of the curve A. This results from the fact that, for the beat frequency under consideration, the short-circuited winding 19 does not permit the voltage across the winding 21 to rise to its maximum value before a succeeding direct-current pulsation in the winding 10 causes the voltage of the winding 21 to be again reduced.

For a higher beat frequency than that above considered, conditions may be illustrated by curve D. The maximum value of curve D occurs at a still later time and is still lower than the maximum value of the curve A.

The operation of the transformer 27, rectifier 31 and relay 32, to cause the initiation of the operation of the paralleling switch 3, is made to depend upon the difference in the fluxes set up by the direct-current windings 25 and 26 in the center leg of the transformers 27: These windings are so connected that the fluxes induced thereby are in opposite directions. As long as these fluxes are unequal, a resulting flux, in one direction or another, will exist in center leg of the core of the trans former 27, and, in accordance with the explanation already given, the voltage across the secondary winding 29 will be reduced to such value that the direct-current voltage of the rectifier 31 will be insufficient to energize the relay 32 to cause it to close its contacts.

When the difference in the fluxes developed by the windings 25 and 26 reaches a predetermined minimum, however, the saturation of the core of the transformer 27 is so reduced that the voltage across the secondary winding 29 is increased and the direct-current output of the rectifier 31 is sufficient to energize the relay 32, which thereupon closes its contact 23 to establish a circuit to the closing coil of the paralleling switch 3.

As may be observed from the consideration of Fig. 1, the flux in the center lug of the core 26 of the reactor 27 is reduced to zero when the direct-current voltages of the rectifiers 23 and 24 are equal, assuming the windings 25 and 26 to have the same resistance and number of turns. As shown in Fig. 2, for a beat frequency corresponding to curve C, the voltage of the rectifier 24, illustrated by curve A, is equal to that of the rectifier 23, shown by curve C, when the two curves intersect, at a time T in advance of zero phase difference, or exact synchronism.

For the beat frequency for which curve D illustrates the variation of the voltage across the winding 21, the direct-current voltages of the rectifiers 23 and 24' are equal at the intersection of the curves A and D, which occurs in advance of synchronism by a time T For still higher beat frequencies, the intersection of the curves occurs at still greater intervals in advance of exact synchronism.

It is apparent, therefore, that the paralleling relay system of my invention causes the operation of the paralleling switch to be initiated in advance of the occurrence of synchronism by a time interval which is proportional to the beat frequency, or the difference in the frequencies of the line and the incoming generator. The system of my invention presents the advantage that, by suitable design of the elements thereof, the closing of the paralleling switch 3 maybe caused to take place at exact synchronism, irrespective of the beat frequency. This result is accomplished by energizing the closing coil of the paralleling breaker in advance of actual synchronism by a time interval proportional to the beat frequency.

A further advantage obtained by the use of my system is that the apparatus required and the circuits involved are simple and relatively inexpensive with systems known heretofore.

I am aware that various changes in my paralleling relay system will occur to those skilled in the art. My system, for instance, may be employed to control the paralleling of a polyphase circuit instead of a single phase circuit in connection with which it is illustrated. The alternating current source 16, furthermore, may be omitted and the primary windings on the reactors energized from the generator buses.

Instead of utilizing the opposing windings 25 and 26 on the center leg of the transformer 27, a single winding may be employed, energized by the difference in the voltages at the direct-current terminals of the rectifiers 23 and 24. The disadvantage of this scheme of connections, however, is that any interruption of the current in the direct-current winding causes the voltage on the relay 32 to increase sufficiently to cause paralleling. .When two opposing windings are employed, however, any interruption of the current to one of them permits the other to saturate the core to prevent a rise of the voltage on the relay so that paralleling cannot occur. The safety factor of the system as disclosed, therefore, is higher than that of the system aboveisuggested.

, Various other changes may, of course, be made in the system as disclosed and I do not intend to be limited to the exact embodiment shown herein except as indicated by the appended claims.

I claim as my invention:

1. In an automatic paralleling system for alternating-current circuits, means for connecting said circuits in parallel when the voltages thereof are in phase, and means responsive to the phase voltages for initiating the operation of said connecting means in advance of the occurrence of phase coincidence by a time interval proportional to the difference between the frequencies of the circuit voltages.

2. A paralleling system for alternatingcurrent circuits comprising a switch for con necting saidcircuits, an operating coil for said switch, and means automatically controlled by the difference in phase angle of the voltage and frequency of the circuits for energizing said coil in advance of-the occurrence of phase coincidence of the circuit voltages by a time interval proportional to the difi'erence of the frequencies of the said voltages.

3. The combination, in a paralleling system for alternating-current circuits, with a circuit closer and means for operating it, of transformers having direct-current and alternating-current windings, means for energizing said direct-current windings in proportion to the vector difference of the voltages of said circuits to vary the voltage across the alternating-current secondary windings when the primary windings are energized, means on one of said transformers for delaying the variations in the voltage across the alternating-current secondary winding thereof and means responsive to equality of the voltages across the alternating-current secondary windings of said transformers for causing the energization of the circuit-closer-operating means. i

4. A paralleling system for alternatingcurrent circuits comprising connecting means for said circuits, transformers having pri-v mary and secondary windings, means for energizing said primary winding by altermating-current, means for varying the voltage across said secondary windings, means for delaying the variations in the voltage across the secondary windings of one transformer, and means responsive to equal- I ity of the voltages across said secondary windings for initiating the operation ofsaid connecting means.

5. In a paralleling system for alternatingcurrent circuits, transformers having alternating-current primary and secondary windings and direct-current saturating windings for varying the voltage across said alternating-current secondary windings, means for'energizing the direct-current windings of: two of said transformers in proportion to the vector difference of the circuit voltages, one of said transformers having means for delaying the variations in its alternatingcurrent secondary voltage, a third transformer being saturated in proportion to the difference of the alternating-current secondary'voltages of said first mentioned transformers, means for energizing all of the transformers, a paralleling relay and means whereby it is energized iii proportion to the current primary and secondary windings and v direct-current saturating windings for vary-. ing the voltage across said alternating current secondary windings, means for energizing the direct-current windings of said transformers in proportion to the vector difference of the voltages of said alternatingcurrent circuits,ione of said transformers having an additional winding for delaying the variation in thealternating-current voltage of its secondary winding eflected by the direct-current winding, of a third transformer having opposing direct-current saturating windings, means for "energizing said opposing direct-current windings in propor tion to the alternating-current secondary voltages of said first-named transformers, a paralleling relay, and means for energizing said relay in'proportion to'the alternatingcurrent secondary voltage of said third trans former.

7. Automatic means for obtaining an advance initiation of a mechanism employed to parallel alternating-current circuits, proportional to the difference in the frequencies of said circuits, whereby they will be paralleled precisely at the instant of exact phase coincidence ofthe circuit voltages, comprising transformers having alternating-current primary and secondary windings and directcurrent saturating windings disposed to vary the voltage across said alternating current secondary windings, rectifiers so connected to said circuits as to supply to said directcurrent windings currents proportional to the'vector difference of the circuit voltages, means-for delaying the variations inthe alternating-current secondary voltage of one of said transformers, and a third transformer having opposing direct-current saturating sud windings, means for supplying its directcurrent windings with currents proportional to the alternating-current secondary voltages of said first-mentioned transformers, a relay for initiating the paralleling operation, and means for energizing said relay by a current proportional to the alternating-current voltage of said last-mentioned transformer.

8. In a paralleling system for alternatingcurrent circuits, the combination with a circuit closer for connecting said circuits and means for operating it, of transformers havin alternating-current primary and secondary windings, and direct-current windings which, when energized, vary the voltage induced in said alternating-current secondary windings, means for energizing the primary windings of the transformers, rectifiers for energizing said direct-current windings in proportion to the vector difference of the voltages of the circuits, means for delaying the variation in the voltage across the alternating-current secondary windings of one of said transformers resulting from the energization of its direct-current winding, and means responsive to equality of the voltages across the alternating-current secondary windings of said transformers for energizing the circuit-closer operating means.

9. A paralleling system for alternatingcurrent circuits comprising a connecting switch provided with an operating coil, a pair of transformers, means for exciting the transformers, means for obtaining a voltage proportional to the vector difference of the circuit voltages, means responsive to said voltage for varying the secondary voltages of the transformers, means associated with one of said transformers for effecting a delay in the variations of its secondary voltage, and means controlled by the secondary voltages of said transformers for effecting the energization of the operating coil of the connecting switch, said means being disposed to effect the actual operation of the switch in response to an equality of the secondary voltages of the transformers.

10. A system for paralleling alternatingcurrent circuits comprising a switch for connecting saidcircuits, a paralleling relay for controlling the operation of said switch, and

means for governing said relay including a plurality of transformers having alternatingcurrent primary and secondary windings and direct-current saturating windings for varying the voltage induced in said alternatingcurrent secondary winding when the primary winding is energized, means for energizing the primary winding, means for supplying to the direct-current windings of said transformers a current proportional to the vector difference of the voltages of the alternatingcurrent circuits, means for delaying the variation of the alternating-current secondary voltage of one of said transformers, athird transformer having opposing direct-current windings, means for supplying to its directcurrent windings currents proportional to the alternating-current secondary voltages of said first mentioned transformers, and means for energizing said paralleling relay in proportion to the alternating-current secondary voltage of said last-mentioned transformer.

11. In a paralleling system for alternatingcurrent circuits, in combination, a connecting s; itch for the circuits, means for effecting the operation of the switch, and means responsive to the vector difference of the phase voltages of the circuits for controlling the operation of said switch-operation-effecting means, said means being further responsive to the difference of the frequencies of the phase voltages of the circuits for varying the time interval occurring between the initiation of the switch-closing operation and phase coincidence of the circuits, thereby to automatically effect a paralleling operation at phase coincidence regardless of the frequency difference of the circuits prior to phase coincidence.

In testimony whereof, I have hereunto subscribed my name this 25th day of January,

PHILLIPS THOMAS. 

